The primary goal of this proposal is to train the applicant as a health professional to become an independent investigator. To achieve this goal, a five-year, mentored training program with heavy didactic coursework in epidemology and biostatistics is described that will lead to a PhD in epidemiology. Six mentors, with expertise in epidemiology, biostatistics, clinical research, cataract and refractive surgery, and theoretical opticas have been selected. The secondary goal of this proposal is to investigate the current inaccuracies of corneal power estimation and intraocular lens (IOL) power calculation in eyes that have undergone myopic refractive surgery and require cataract extraction and IOL placement. Current methods used to calculate IOL power in non-surgical eyes are inaccurate post-refractive surgery and cause unintentional hyperopia in up to 83-100% of eyes post-cataract surgery. Historical clinical data, the "gold standard" in estimating corneal power post-refractive surgery is rarely available, especially decades later when cataract surgery is necessary. We propose to: a) identify a theoretical model using a cross-sectional study that will allow us to evaluate and refine the accuracy and precision of a contact lens overrefraction method in estimating corneal refractive power without using cataractous eyes; and b) we will test the hypothesis that our refined contact lens over-refraction method can be used in calculating IOL power in eyes that have developed cataracts. We will use a prospective cohort study to compare refractive complications post-cataract surgery between post-refractive surgery patients and cataractous eyes with normal corneas. Refractive surgery is a common method of vision correction, with at least 1.5 million procedures in 2000, and as many as 26.5 million within the next dozen years. Hence, it is critical that an accurate, precise and simple method to estimate corneal power and calculate IOL power is developed. The long-term objective to this research is to contribute to the knowledge of IOL power determination in post-refractive surgery patients.